You can add meetings with multiple CRM records from your Calendar section - as new event (see more page to add CRM records to the event). The event will appear in your calendar & will be shown as meeting activity in each assigned CRM record's details page (but you won't see that this meeting is multiple from the CRM record's page, only from the calendar's section)

Thanks for your question. The call report\details form does not allow to add more than one contact since the call is performed with one party only, not with several. I see what you mean - that you may need to add other CRM records that may be connected to the call, we'll consider your suggestion for the future updates. Currently the system logic does not support that.